1. Technical Field
The present invention relates to a magnetic circuit for a speaker used in audio equipment and video equipment for various purposes including in-car applications, as well as a speaker.
2. Background Art
FIG. 11 is a cross-sectional view of a magnetic circuit in a conventional speaker. Magnetic circuit 101 in the conventional speaker is configured by yoke 102 and bond magnet 103 fixed on yoke 102. Bond magnet 103 is in an annular shape, and includes through hole 103A in its central portion. Further, bond magnet 103 is configured such that the south pole is provided on an inner sidewall of through hole 103A, and the north pole is provided on upper section of side surface 103B. In other words, a magnetic field is oriented in a radial direction of bond magnet 103.
At this time, a magnetic flux loss increases when the north pole provided on upper section of side surface 103B is brought into contact with yoke bottom 102B. Therefore, the cross-section of bond magnet 103 is T-shaped, and bond magnet 103 is disposed such that its upper portion has a greater diameter than that of its lower portion. With this, magnetic gap 104 is provided between upper section of side surface 103B of bond magnet 103 and yoke side wall 102A.
Next, a description will be given of one example of a method for causing bond magnet 103 as described above to be magnetically oriented. A cavity of a mold for conventional bond magnet 103 is made of a non-magnetic material, and in the shape of bond magnet 103. Further, bond magnet 103 is formed by filling the cavity with a resin containing magnetic powder.
However, a face of the cavity corresponding to upper section of side surface 103B is provided as an annular magnetic body. Accordingly, the annular magnetic body is provided with a hole having a shape of upper section of side surface 103B, and upper section of side surface 103B is formed by an inner face of the hole in the annular magnetic body. Further, a stick-shaped magnetic body is provided at a position corresponding to through hole 103A, and through hole 103A is formed by this second magnetic body. Then, the magnetic orientation of bond magnet 103 is achieved by causing magnetism to pass from the stick-shaped magnetic body toward the annular magnetic body when molding.
Here, for example, PTL 1 is known as prior art document information regarding the invention of this application.